Dendrochronological research

Welcome to dendrochronological www pages of the Department of Geosciences and Geography, University of Helsinki!

The field of dendrochronology comprises various types of analyses on annual rings of trees, tree rings. One of the main principles of dendrochronology is cross-dating. Dendrochronologists analyze tree-rings by their common growth behaviour and, as initial step of each analyses, cross-match the wide and narrow tree-rings among the array of samples. One tree-ring chronology may consist of tens or hundreds, even thousands, of individual tree-ring series of the same species from a given region. Series are averaged annually to form reliable records of past growth changes. Subsequent to cross-dating, tree-ring chronology becomes dated with absolute accuracy. Climatic and environmental factors influence the growth of tree-rings from inter-annual to millennial time-scales. This creates possibility to date the past climatic and environmental events with highest possible precision of all geological records!

Tree-ring research conducted at the Department of Geosciences and Geography has its roots in the study of subfossil pinewood archives. Scots pine (Pinus sylvestris L.) megafossils remain preserved in the bottom sediments small lakes, peat bogs and as dead standing trees (snags). Additional tree-ring material can be obtained from historical buildings. Theory of cross-dating is a key to built composite chronologies from living, historical and subfossil tree-rings. Megafossil collection from northernmost Lapland covers the past 76 centuries being one of the longest continuous tree-ring chronologies in the world. At the same time, this chronology is probably the longest absolutely dated and annually resolved temperature proxy record. Sample collection was largely intensified in the 1990s in collaboration with the Finnish Forest Research Institute and SAIMA Centre for Environmental Sciences. Over those years, the research was led by the professor Matti Eronen (1944-2016) who had started the research of collecting subfossil pine samples in Finnish Lapland already in the early 1970s. Since then, the tree-ring research has continued to focus primarily on climatic and palaeoclimatic targets. Meanwhile, the research topics have also increased in number to cover the different subfields of dendrochronology. This research has been conducted by those researchers who share the collegial identification of the this dendrochronological school. Samuli Helama is currently at the Natural Resources Institute, Rovaniemi, and also acting as a docent at the department. Jari Holopainen has recently continued his activities at the University of Eastern Finland. Marc Macias-Fauria is acting as an associate professor at the University of Oxford. Morever, Alar Läänelaid, whose dissertation work was the first tree-ring based PhD thesis at the department, acts as an associate professor at the University of Tartu.

More recently, this tree-ring work has continued under the CARATE- ja QUANOMAL-projects (link), funded by the Academy of Finland, which have been research consortiums between the Laboratory of Chronology (Univeristy of Helsinki) and the Natural Resources Institute Finland. These projects have advanced the use of Finnish dendrochronological archives to analyse isotopes from cross-dated tree-ring cellulose, to build long chronologies of stable carbon (13C) and oxygen (18O) and of radiocarbon (14C) to infer the changes in plant ecophysiology, and to assess past and ongoing climate variability and the historical/prehistoric solar superstroms. Importantly, this work has built on the legacy of subfossil tree-ring analyses that now itself has an intellectual, departmental history of nearly half a century.

The basis of our dendrochronological research is the compound interpretation of living tree and subfossil tree-rings, their variability and factors behind their behaviour. The research can be divided into several different subfields as follows:

1) Dendrochronology: constructing new tree-ring chronologies

2) Dendroclimatology: studying the relationships between tree-rings and climate

3) Dendroecology: studying the relationships between tree-rings and ecological factors

4) Palaeoclimatology: reconstructing the past climates using tree-ring chronologies

5) Palaeoecology: interpreting the past environments from tree-ring based records

6) Time-series analysis is used in all aforementioned (1-5) subfields of dendrochronology.

Students aiming for dendrochronological thesis (Bachelor, Master, Licentiate or Ph.D.) should familiarize himself/herself with at least the basic concepts of time-series analysis!

Lecture course in Dendrochronology, 54252, has been lectured at the Department of Geosciences and Geography, several times over the past years. Teaching language of the course has been, most recently, English (link).

Doctoral dissertations

May 2008
"Ecological processes and large-scale climate relationships in northern coniferous forests"
Marc Macias Fauria

November 2006

"Reconstructions of past climates from documentary and natural sources
in Finland since the 18th century"
Jari Holopainen

June 2004
"Millennia-long tree-ring chronologies as records of climate variability in Finland"
Samuli Helama

November 2002
"Tree-ring dating in Estonia"
Alar Läänelaid

Essential text-books

Speer, J. 2010. Fundamentals of Tree-Ring Reearch. University of Arizona Press, 333 p.

Cook E.R. & Kairiukstis L.A. (Editors) 1990: Methods of Dendrochronology. Kluwer Academic Publishers, 394 pp.

Hughes M.K., Kelly P.M., Pilcher J.R., Lamarche V.C., Jr. (Editors) 1982: Climate from tree rings. Cambridge University Press, 223 pp.

Fritts H.C. 1976: Tree Rings and Climate. Academic Press, 567 pp.